Sex determination: insights from the human and animal models suggest that the mammalian Y chromosome is uniquely specialised for the male's benefit

Our children will normally be born as either girls or boys and most of us appreciate that the father determines sex. The very rare occurrence of sex-reversed and inter-sex offspring as well as recent research into the genetic causes of male infertility has fostered a rapid expansion in our understanding of the molecular genetic basis of sex determination in humans and other animals. This overview of the field focuses on where the discovery of SRY, the mammalian male sex determining gene and other genes involved in the cascade of events that orchestrate sex determining mechanisms, is leading us, both in reproductive research and in their continuing evolution in mammals and other animals. Comparisons between different mechanisms illuminates highly conserved evolutionary aspects of the genes involved and provides insights into the force that drives the acquisition and adoption of particular sex-determining genes. We shall also see that sex determination and Y-associated human infertility are linked phenomena and that the evolution of the mammalian Y chromosome has played, and continues to play, a pivotal role in this linkage.